The termination of an optical fiber with a connector in a field environment generally is a costly and labor intensive process, and has thus slowed the acceptance of fiber optics in both local and wide area networks, as well as in other applications. Additionally, connectors for use in forming terminations of the fiber are generally of such a nature that only limited numbers of individual fibers can be terminated in, for example, a day. Connectors presently in use often require that special tools be present at the job site. Thus, where the fiber end being connected is held within the connector by means of an ultra-violet or heat cured epoxy, a source of ultra-violet light or of heat must necessarily form a part of the tool kit of the technician making the termination. Also, the use of epoxy is time consuming. Generally, when, for example, a heat cured epoxy has been applied, the entire connector assembly must be heat cured for several minutes, and then several more minutes are involved until the assembly is cooled sufficiently for the fiber tip to be polished.
The prior art is rife with connector designs that have been proposed and marketed and that are aimed at increasing installation efficiency through reduction or elimination of one or more of the aforementioned problems. One such approach involves the use of a hot melt glue instead of a heat cured epoxy to affix the fiber to the connector. In this arrangement, the technician places the connector in a heater for a short time to melt a premeasured amount of glue previously placed within the connector. The fiber is then inserted, and, after the connector has cooled for a short time, the tip of the fiber can be polished. Such a hot melt connector has been found to reduce the time involved to completion, and is relatively simple to assemble. However, it is not recommended for use in installation subject to high temperatures. Another approach to the elimination of dependence upon epoxy to affix the fiber to the connector or termination has been the use of crimp-on connectors which form a mechanical connection between the connector and the fiber. Unless the crimping portion grasps the fibers firmly, pistoning of the fiber may occur, and the integrity of the connector jeopardized.
In all of the foregoing arrangements, it is necessary, after the fiber is affixed in place, to cleave and polish that end of the fiber intended to mate with the fiber with which it is to be connected. This, too, requires the use of special tools, and at least some measure of experience and skill on the part of the technician. In U.S. Pat. No. 5,082,377 of Jarrett et al., there is shown an optical fiber connector which eliminates the need for cleaving and polishing the end of the fiber, thereby reducing both preparation time and reliance on the skill of the technician. The basic component of the connector which makes this possible is a cylindrical body or plug having an axial bore extending therethrough. A short optical stub member of a material having the same index of refraction as the optical fiber to be terminated is located within the bore with one end flush with the end of the cylindrical body, and both are ground and polished to produce a uniformly flat front face. The rear end of the stub, within the bore, is a planar surface. This much of the connector, including the other mechanical and structural elements thereof is manufactured and pre-assembled at the factory, for example, and can be carried into the field by the technician. When an optical fiber is to be terminated by the connector, the end of the fiber is stripped of its protective coating and the end face cleaved. A thin metered layer of index matching polymerizable resin is then placed on the end face of the fiber which is inserted into the bore until it reaches the rear end face of the stub member. The resin is then cured, as by ultraviolet radiation or heat, to bind the fiber end to the stub.
The use of a polymerizable resin for index matching and securing the fiber within the connector, as in the connector of the Jarrett et al. patent, has numerous drawbacks. The resin itself tends to develop numerous microscopic bubbles which degrade the index match, thereby increasing insertion loss. Also, because of the extremely small area of fixation of the end of the fiber to the end of the stub, the cemented joint is not reliable, especially if tensile forces are applied, as they usually are in such connection arrangements, thus placing a strain upon the joint. In order for there to be as perfect an axial alignment as possible between the stub and the fiber, the bore through which the fiber is inserted is only fractions of a micron greater in diameter than the fiber, thus keeping it aligned within the stub. However, such a close fit does not provide space into which the excess resin can spread when it is compressed between the fiber end and the stub end. As a consequence, the resin, which can only be compressed a certain amount, can prevent the fiber end from closely abutting the stub end, which, ideally, is the preferred relationship for minimizing transmission losses.
An optical fiber connector that is easily and inexpensively produced, that can be quickly and easily and thereby economically installed in the field by relatively unskilled personnel, which has low insertion loss and which can withstand the tensile forces ordinarily encountered by connectors during and after installation would clearly be an advance over the connector arrangements which characterize the present state of the art.